The post on Garter Snakes in
Newfoundland attracted much attention, so I investigated high latitude garter snakes
a bit further. As far as I can see this news report is the first evidence of
snakes from Newfoundland. But, in central and western Canada garter snakes have
been known to reach relatively high latitudes, latitudes, higher than that report in Newfoundland.
Garter Snakes are quite cold
tolerant and range farther north than any other North American snakes. They are
also capable of submerged hibernation, a poorly studied behavior (Murphy 2010)
and one that undoubtedly increases their survival at high latitudes.
John Richardson (1851) [in Bauer
and Russell, 2001] appears to be the first to report garter snakes in central Saskatchewan,
when he observed garter snakes at Serpent Lake. The earliest reference to
garter snakes in Alberta appears to be Ǽmilius Simpson’s journal written in
1826. He was traveling on the North Saskatchewan River and passed the
confluence with the Stone River at noon, he was at 53º45’34”N, 110º40’W and the
temperature was 75ºF. The bank was limestone and clay, and he wrote, “…we
passed great numbers of small striped Black & green snake swimming from the
South to the North Bank of the River & strewed along the Sandy Beach on the
North Shore, as if enjoying the powerful influence of the Sun, & it
appeared that those crossing were leaving the cold of the Northern aspect to
gain the more pleasing heat of the southern exposure.”
Bauer and Russell (2001) examined
Simpson’s account and adjusted his co-ordinates, suggesting that they were
actually, 53°45’15”N, 111°10’W and the area Simpson passed at noon is now known
as Fort Island. Three species of garter snakes occur in Alberta: the Plains Garter
Snake, Thamnophis radix, the
Wandering Garter Snake, T elegans,
and Red-sided Garter Snake, T sirtalis.
The Wandering Garter Snake is restricted to the southwestern Albert in the
Rocky Mountain and prairie biomes, but specimens are occasionally found much
further north, and the species is often associated with rivers. All modern
records from the vicinity of Fort Island are attributable to T radix, and most are from localities in
Aspen Parkland or Prairie, with a few Plains Garter Snakes collected in the Boreal
Forest Biome north of the North Saskatchewan River. Simpson’s color description
describes both the Red-sided Garter Snake and the Plains Garter Snake and both
species are associated with water and swimming behavior, T. sirtalis more so.
Larsen et al. (1993) studied this
snake at Wood Buffalo National Park (59º49'N, 112º W) in the Northwest Territories,
Canada. This is the highest known latitude for Thamnophis sirtalis. Thet found females rarely gave birth in 2
successive years. Female snakes matured at larger body sizes (570 mm) than
snakes in Manitoba (527 mm), and they had smaller litter sizes than Manitoba
females. The authors conclude that there is no single suite of life history
traits for northern populations of garter snakes. The smallest gravid female
they observed was 670 mm, but found a 570 mm female that had mated.
But are there garter snakes in
Alaska? McDonald (2003) noted that the valleys of the Stikine River and Taku
River (and perhaps Unuk River) could potentially allow Thamnophis access to the coast from the interior British Columbia,
however, it remains unclear if snakes occur in these drainages. A preliminary
search for garter snake records from major drainages that flow into coastal
Alaska did not produce any evidence of their presence. McDonald reports that a
resident of Telegraph Creek, BC, stated that he could not recall anyone ever
seeing a snake in the area. The Common Garter Snake (Thamnophis sirtalis) has been reported north of Terrace, British
Columbia, in the watersheds of the Nass and Skeena rivers, and along the
eastern side of the province as far north as the Peace River District (Gregory
and Campbell 1984). The Western Terrestrial Garter Snake (T. elegans) is found
along the British Columbia coast, including Vancouver Island, as far north as
the Skeena River Basin, and east of the Rockies as far north as the Peace River
District (Gregory and Campbell 1984).
In eastern
Canada the Maritime Garter Snake, Thamnophis
sirtalis pallidulus, covers a considerable amount of geography. Bleakney
(1959) redescribed the subspecies Thamnophis
sirtalis pallidulus noting that its coloration was distinct over a large
area and that it shows sexual dimorphism in ventral scale and subcaudal counts,
commenting that T. s. pallidulus from
Nova Scotia have 6 to 7 fewer ventral scales and 7 to 10 fewer subcaudal scales
than T. s. sirtalis. And, he writes, “The
subspecies [T. s. pallidulus] ranges
throughout the Atlantic Provinces (exclusive of Newfoundland), westward into
New Hampshire and thence northwestward to James Bay, and eastward again along
the north shore of the Gulf of St. Lawerence.”
Barnes et al.
(2006) examined the ecology and morphology of the population of the Maritime
Garter Snake on Georges Island, Nova Scotia and marked 391 garter snakes,
reported a male to female ratio of 0.8:1.0; and a population density for adult
snakes of 120/ha. They found these snakes to be exceptionally docile, and the
population contained melanistic individuals. Perhaps most remarkable they found
female snakes reproductively active at a body length of 350 mm. This is quite
small, Fitch (1965) reported that Kansas males mature at about 400 mm, and
females mature at about 500 mm or 15 months of age. It seems likely that high
latitude populations will grow more slowly and mature at smaller sizes and
older ages due to abbreviated season of activity, but the studies done to date
show a range of sizes at maturity for female snakes.
Gregory and
Larsen (1993) studied geographic variation in litter size and neonate size in
several populations of garter snakes (T.
sirtalis) across Canada and found gravid females differed significantly in
body size between the sites. Even after they corrected for inter-site
differences in female body size, there were highly significant differences in
litter size and neonate size. Populations with large litters tended to have
small progeny, but they found only weak evidence of a "tradeoff"
between neonate size and litter size within populations. Snakes from eastern
Canada were relatively small at maturity and produced large litters of very
small young, while those from western Canada were usually large and produced
smaller litters (for a given body size) of larger young.
The map above
shows the Newfoundland Record (red Triangle), the Wood Buffalo population (grey
square), the approximate range of T. s. pallidulus
(blue shading) and some high latitude locations for sirtalis on the west coast (black spheres).
This is not an
exhaustive compilation of high latitude Thamnophis. If you know of others leave
a comment.
References
Barnes, S. M.,
C. M. Dubesky, and T. B. Herman. 2006. Ecology and morphology of Thamnophis sirtalis pallidulus (Maritime
Garter Snakes) on Georges Island, Nova Scotia. Northeastern Naturalist
13(1):73-82.
Bauer, A. M. and
A. P. Russell. The First Record of
Reptiles in Alberta: AEmilius Simpson's Journal of 1826 Herpetological Review
32(3):174-176
Bleakney, S.
1959. Thamnophis sirtalis sirtalis
(Linnaeus) in eastern Canada, redescription of T. s. pallidula Allen. Copeia 1959(1):52-55.
Fitch, H. S.
1965. An ecological study of the garter snake, Thamnophis sirtalis. University of Kansas Publication, Museum of
Natural History 15:493-564.
Gregory, P. and
K. W. Larsen. 1993. Geographic variation in reproductive characters among
Canadian populations of the common garter snake (Thamnophis sirtalis). Copeia 1993(4):946-958.
Larsen, K. W., P. T. Gregory, and
R. Antoniak. 1993. Reproductive ecology of the common garter snake Thamnophis sirtalis at the Northern Limit
of its range. American Midland Naturalist 129:336-345.
McDonald, S. O. 2003. Amphibians
and Reptiles of Alaska, A Field Handbook. http://www.alaskaherps.info/
Murphy, J. C.
2010. Secrets of the Snake Charmer, Snakes in the 21st Century.
Bloomington: iUniverse. 420 pages.